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Lecture 14: Distributed Multimedia Systems Haibin Zhu, PhD. Assistant Professor Department of Computer Science Nipissing University © 2002 Contents Introduction Characteristics of multimedia data Quality of service management Resource management Stream adaptation Summary

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Lecture 14 distributed multimedia systems l.jpg

Lecture 14:Distributed Multimedia Systems

Haibin Zhu, PhD.

Assistant Professor

Department of Computer Science

Nipissing University

© 2002


Contents l.jpg
Contents

  • Introduction

  • Characteristics of multimedia data

  • Quality of service management

  • Resource management

  • Stream adaptation

  • Summary

2


Learning objectives l.jpg
Learning objectives

  • To understand the nature of multimedia data and the scheduling and resource issues associated with it.

  • To become familiar with the components and design of distributed multimedia applications.

  • To understand the nature of quality of service and the system support that it requires.

  • To explore the design of a state-of-the-art, scalable video file service; illustrating a radically novel design approach for quality of service.

*

3


A distributed multimedia system l.jpg

Video camera

and mike

Local network

Local network

Wide area gateway

Video

Digital

server

TV/radio

server

A distributed multimedia system

Figure 15.1

  • Applications:

    • non-interactive: net radio and TV, video-on-demand, e-learning, ...

    • interactive: voice &video conference, interactive TV, tele-medicine, multi-user games, live music, ...

*

4


Multimedia in a mobile environment l.jpg
Multimedia in a mobile environment

  • Applications:

    • Emergency response systems, mobile commerce, phone service, entertainment, games, ...

Global System for Mobile Communications

*

5


Characteristics of multimedia applications l.jpg

At the right timeand in the right quantities

Characteristics of multimedia applications

  • Large quantities of continuous data

  • Timely and smooth delivery is critical

    • deadlines

    • throughput and response time guarantees

  • Interactive MM applications require low round-trip delays

  • Need to co-exist with other applications

    • must not hog resources

  • Reconfiguration is a common occurrence

    • varying resource requirements

  • Resources required:

    • Processor cycles in workstations

    • and servers

    • Network bandwidth (+ latency)

    • Dedicated memory

    • Disk bandwidth (for stored media)

*

6


Application requirements l.jpg
Application requirements

  • Network phone and audio conferencing

    • relatively low bandwidth (~ 64 Kbits/sec), but delay times must be short ( < 250 ms round-trip)

  • Video on demand services

    • High bandwidth (~ 10 Mbits/s), critical deadlines, latency not critical

  • Simple video conference

    • Many high-bandwidth streams to each node (~1.5 Mbits/s each), high bandwidth, low latency ( < 100 ms round-trip), synchronised states.

  • Music rehearsal and performance facility

    • high bandwidth (~1.4 Mbits/s), very low latency (< 100 ms round trip), highly synchronised media (sound and video < 50 ms).

http://www.topsavings.net/dedicated-t-1.html

*

7


System support issues and requirements l.jpg
System support issues and requirements

  • Scheduling and resource allocation in most current OS’s divides the resources equally amongst all comers (processes)

    • no limit on load

    • \ can’t guarantee throughput or response time

  • MM and other time-critical applications require resource allocation and scheduling to meet deadlines

    • Quality of Service (QoS) management

      • Admission control: controls demand

      • QoS negotiation: enables applications to negotiate admission and reconfigurations

      • Resource management: guarantees availability of resources for admitted applications

    • real-time processor and other resource scheduling

*

8


Characteristics of typical multimedia streams l.jpg

Data rate

Sample or frame

(approximate)

frequency

size

Telephone speech

64 kbps

8 bits

8000/sec

CD-quality sound

1.4 Mbps

16 bits

44,000/sec

Standard TV video

120 Mbps

up to 640

x

480

24/sec

(uncompressed)

pixels

x

16 bits

Standard TV video

1.5 Mbps

variable

24/sec

(MPEG-1 compressed)

HDTV video

1000–3000 Mbps

up to 1920

x

1080

24–60/sec

(uncompressed)

pixels

x

24 bits

HDTV video and DVD

10–30 Mbps

variable

24–60/sec

MPEG-2 compressed)

Characteristics of typical multimedia streams

Figure 15.3

*

10


Typical infrastructure components for multimedia applications l.jpg

PC/workstation

PC/workstation

Windowsystem

Camera

Component

Bandwidth

Latency

Loss rate

Resources required

K

H

G

A

Codec

Codec

Out:

10 frames/sec, raw video

Zero

Camera

L

B

Microphones

640x480x16 bits

Mixer

Network

connections

A

Codec

In:

10 frames/sec, raw video

Interactive

Low

10 ms CPU each 100 ms;

Screen

C

Video

file

system

Video

store

M

D

Out:

MPEG-1 stream

10 Mbytes RAM

Codec

:

multimedia stream

Window

system

White boxes represent media processing components, many of which are implemented in software, including:

B

Mixer

In:

2 44 kbps audio

Interactive

Very low

1 ms CPU each 100 ms;

Out:

1 44 kbps audio

1 Mbytes RAM

codec: coding/decoding filter mixer: sound-mixing component

H

Window

In:

various

Interactive

Low

5 ms CPU each 100 ms;

system

Out:

50 frame/sec framebuffer

5 Mbytes RAM

K

Network

In/Out:

MPEG-1 stream, approx.

Interactive

Low

1.5 Mbps, low-loss

connection

1.5 Mbps

stream protocol

L

Network

In/Out:

Audio 44 kbps

Interactive

Very low

44 kbps, very low-loss

stream protocol

connection

Typical infrastructure components for multimedia applications

Figures 15.4 & 15.5

  • This application involves multiple concurrent processes in the PCs

  • Other applications may also be running concurrently on the same computers

  • They all share processing and network resources

*

11


Quality of service management l.jpg
Quality of service management

  • Allocate resources to application processes

    • according to their needs in order to achieve the desired quality of multimedia delivery

  • Scheduling and resource allocation in most current OS’s divides the resources equally amongst all processes

    • no limit on load

    • \ can’t guarantee throughput or response time

*

12


Elements of quality of service qos management l.jpg
Elements of Quality of Service (QoS) management

  • Admission control: controls demand

  • QoS negotiation: enables applications to negotiate admission and reconfigurations

  • Resource management: guarantees availability of resources for admitted applications

  • real-time processor and other resource scheduling

13


Figure 15 5 qos specifications for components of the application shown in figure 15 4 l.jpg

Component

Bandwidth

Latency

Loss rate

Resources required

Out:

10 frames/sec, raw video

Zero

Camera

640x480x16 bits

A

Codec

In:

10 frames/sec, raw video

Interactive

Low

10 ms CPU each 100 ms;

Out:

MPEG-1 stream

10 Mbytes RAM

B

Mixer

In:

2 44 kbps audio

Interactive

Very low

1 ms CPU each 100 ms;

Out:

1 44 kbps audio

1 Mbytes RAM

H

Window

In:

various

Interactive

Low

5 ms CPU each 100 ms;

system

Out:

50 frame/sec framebuffer

5 Mbytes RAM

K

Network

In/Out:

MPEG-1 stream, approx.

Interactive

Low

1.5 Mbps, low-loss

connection

1.5 Mbps

stream protocol

L

Network

In/Out:

Audio 44 kbps

Interactive

Very low

44 kbps, very low-loss

connection

stream protocol

Figure 15.5QoS specifications for components of the application shown in Figure 15.4

14


The qos manager s task l.jpg
The QoS manager’s task

Figure 15.6

*

15

*


Qos parameters l.jpg
QoS Parameters

Bandwidth

  • rate of flow of multimedia data

    Latency

  • time required for the end-to-end transmission of a single data element

    Jitter

    • variation in latency :– dL/dt

      Loss rate

  • the proportion of data elements that can be dropped or delivered late

*

16


Managing the flow of multimedia data l.jpg
Managing the flow of multimedia data

  • Flows are variable

    • video compression methods such as MPEG (1-4) are based on similarities between consecutive frames

    • can produce large variations in data rate

  • Burstiness

    • Linear bounded arrival process (LBAP) model:

      • maximum flow per interval t = Rt + B (R = average rate, B = max. burst)

    • buffer requirements are determined by burstiness

    • Latency and jitter are affected (buffers introduce additional delays)

  • Traffic shaping

    • method for scheduling the way a buffer is emptied

*

17


Slide17 l.jpg

Protocol version

Maximum transmission unit

Figure 15.8 The RFC 1363 Flow Spec

Token bucket rate

Token bucket size

Bandwidth:

burstiness

Maximum transmission rate

maximum rate

Delay:

Minimum delay noticed

acceptable latency

acceptable jitter

Maximum delay variation

percentage per T

Loss:

Loss sensitivity

maximum consec-utive loss

T

Burst loss sensitivity

value

Loss interval

Quality of guarantee

50Mbps

150ms

<1/1000

18


Traffic shaping algorithms leaky bucket algorithm l.jpg

(a) Leaky bucket

Traffic shaping algorithms – leaky bucket algorithm

Figure 15.7

analogue of leaky bucket:

  • process 1 places data into a buffer in bursts

  • process 2 in scheduled to remove data regularly in smaller amounts

  • size of buffer, B determines:

    • maximum permissible burst without loss

    • maximum delay

process 1

process 2

*

19


Traffic shaping algorithms token bucket algorithm l.jpg

(b) Token bucket

Token generator

Traffic shaping algorithms – token bucket algorithm

Figure 15.7

Implements LBAP

  • process 1 delivers data in bursts

  • process 2 generates tokens at a fixed rate

  • process 3 receives tokens and exploits them to deliver output as quickly as it gets data from process 1

    Result: bursts in output can occur when some tokens have accumulated

process 1

tokens: permits to place x bytes into output buffer

process 2

process 3

*

20


Admission control l.jpg
Admission control

Admission control delivers a contract to the application guaranteeing:

For each computer:

  • cpu time, available at specific intervals

  • memory

    Before admission, it must assess resource requirements and reserve them for the application

  • Flow specs provide some information for admission control, but not all - assessment procedures are needed

  • there is an optimisation problem:

    • clients don't use all of the resources that they requested

    • flow specs may permit a range of qualities

  • Admission controller must negotiate with applications to produce an acceptable result

    • For each network connection:

      • bandwidth

      • latency

    • For disks, etc.:

      • bandwifth

      • latency

    *

    21


    Resource management l.jpg
    Resource management

    • e.g. for each computer:

      • cpu time, available at specific intervals

      • memory

    • Scheduling of resources to meet the existing guarantees:

      Fair scheduling allows all processes some portion of the resources based on fairness:

      • E.g. round-robin scheduling (equal turns), fair queuing (keep queue lengths equal)

      • not appropriate for real-time MM because there are deadlines for the delivery of data

        Real-time scheduling traditionally used in special OS for system control applications - e.g. avionics. RT schedulers must ensure that tasks are completed by a scheduled time.

        Real-time MM requires real-time scheduling with very frequent deadlines.

        Suitable types of scheduling are:

        Earliest deadline first (EDF)

        Rate-monotonic

    *

    22


    Slide22 l.jpg

    EDF(Earliest Deadline First) scheduling

    Each task specifies a deadline T and CPU seconds S to the scheduler for each work item (e.g. video frame). EDF scheduler schedules the task to run at least S seconds before T (and pre-empts it after S if it hasn't yielded).

    It has been shown that EDF will find a schedule that meets the deadlines, if one exists. (But for MM, S is likely to be a millisecond or so, and there is a danger that the scheduler may have to run so frequently that it hogs the cpu).

    Rate-monotonic scheduling assigns priorities to tasks according to their rate of data throughput (or workload). Uses less CPU for scheduling decisions. Has been shown to work well where total workload is < 69% of CPU.

    23


    Stream adaptation scaling and filtering l.jpg

    Source

    Targets

    High bandwidth

    Medium bandwidth

    Low bandwidth

    Stream adaptation: Scaling and filtering

    Figure 15.9

    • Scaling reduces flow rate at source

      • temporal: skip frames or audio samples

      • spatial: reduce frame size or audio sample quality

    • Filtering reduces flow at intermediate points

      • RSVP is a QoS negotiation protocol that negotiates the rate at each intermediate node, working from targets to the source.

    • The Principle of BitTorrent (http://download.bitcomet.com/doc/principle.htm)

    *

    24


    Qos and the internet l.jpg
    QoS and the Internet

    • Very little QoS in the Internet at present

      • New protocols to support QoS have been developed, but their implementation raises some difficult issues about the management of resources in the Internet.

    • RSVP(http://www.isi.edu/div7/rsvp/rsvp.html)

      • Network resource reservation

      • Doesn’t ensure enforcement of reservations

    • RTP (http://www.cs.columbia.edu/~hgs/rtp/)

      • Real time data transmission over IP

    • need to avoid adding undesirable complexity to the Internet

    • IPv6 has some hooks for it

    25



    Video conferencing l.jpg
    Video conferencing

    • Video conferencing applications can also support:

      • Text chat

      • Document sharing (exchanging files)

      • PowerPoint

      • Application sharing (running the same program, viewing at the same content)

    • frequently there is a way for any participant to control the program

      • Electronic white board – everyone can view what

    • someone writes and draws

    • The word “Collaboration” appears a lot in docs

    27


    Video conferencing27 l.jpg
    Video conferencing

    • Desktop (computer) videoconferencing can be donethrough applications such as

      • Netmeeting (Windows 2000 and XP) –http://www.microsoft.com/windows/netmeeting/

      • Windows Messenger (Windows XP) –http://www.microsoft.com/windowsxp/windowsmessenger/

      • MSN Messenger (Windows) - http://messenger.msn.com/iChat (Apple) - http://www.apple.com/ichat/

    28


    Video conferencing28 l.jpg
    Video conferencing

    • the clients we have mentioned are mainly used for “Instant Messaging”

    • IM is an exchange of text between two or more people who are online at the same time

    • supports group interaction

    • a conversation by typing instead of speaking

    • this is great for short conversations but doesn’t support extended discussion well

    • moving from text to audio and video makes the interaction much more natural

    29



    Video conferencing30 l.jpg
    Video conferencing

    • Can buy videoconferencing appliances that plug into your computer. They come with:

      • camera

      • microphone

      • speaker

      • encoding of video and audio streams done in hardware

      • software to drive it all

    • load on your PC for encoding is then quite small

    31


    Video conferencing31 l.jpg
    Video conferencing

    • Video conferencing is a technology in which video and audio streams are transmitted among the various geographically separated participants in a meeting.

    • Typically this is done through a room which has been set up by a telephone company

    • booking the room also books an operator from the phone company to run the meeting for you

    32


    Summary l.jpg
    Summary

    • MM applications and systems require new system mechanisms to handle large volumes of time-dependent data in real time (media streams).

    • The most important mechanism is QoS management, which includes resource negotiation, admission control, resource reservation and resource management.

    • Negotiation and admission control ensure that resources are not over-allocated, resource management ensures that admitted tasks receive the resources they were allocated.

    • Video conferences

    33


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